Production of high vacua



"JX". TXLLS ET PRODUCTIGN OF HIGH 'VACUA Filed Feb. 9, 1944 5Sheets-Sheet l INVENTORS.

July 30, 1945- .,s. w. TILLS ET AL PRODUCTION OF HIGH VACUA 1944 3Sheets-Sheet 2 Filed Feb. 9

July 30, 1946.

J. w. 'nLLs rs1-AL 2,404,997

PRODUCTION OF HIGH VACUA kFiled Feb,l 9, 1944 3 sheets-sheet 5 PatentedJuly 30, 1946 PRODUCTION F HIGH VACUA John William Tills, Upton,

Hoylake, Wirral, and

Wirral, England Wirral, John B. Lovatt, Frank C. Potts, Upton,

Application February 9, 1944, Serial No. 521,725 In Great BritainNovember 12, 1943 12 Claims.

This invention relates to the production of high vacua, and has for oneobject the attainment of very low pressures which are substantiallyindependent of the vapour pressure of any working fluid associated withthe pumping system.

Another object is to provide positive pumping action of gases at reducedpressures by ionising said gases and submitting the ionised gases to theaction of electrostatic and/or electromagnetic elds.

A further object of the invention is to provide X-ray means forirradiating the gases to produce ionisation.

vA still further object is to provide a selfcontained pumping unitembodying X-ray means for ionisation of gas. and including electrodesmaintained at high electrostatic potential suitably protected andenclosed for the convenience and safety of the operator.

v'I'hese yand lother objects will be apparent after perusal of theappended description with reference to the annexed drawings in which:

Fig. 1 illustrates diagrammatically a side view of one form of migrationpump.

Fig. 2 shows an alternative form. Fig. 3 is a side elevation of anapparatus including a backing pump and the migration pump of Fig. 2.

v VAn X-ray tube l I (Fig. 1) is arranged to irradiate gas in a .tubularglass migration cham- -ber I2 having a high vacuum connexion I3 andelectrodes I4,.I4' between which an electrostatic eld of high potentialgradient is provided by connecting the electrodes to opposite poles of ahigh voltage source of direct current.

y The moulded flanged ends I5, I 5 of the tube are, secured respectivelyby split conical joint rings I1, II to the inlet conduit ilanges ofdiffusion pumps I8, I8 whose outlet conduits are similarly jointed atI9, I9 to the ends of a glass 'If-piece 20 having a backing pumpconnexion ZI.

. The diffusion pumps orrparts thereof may also serve as electrodes, inwhich case, pump I1 for example would be connected either to electrode`I4 or to a pole of a higher voltage supply of the same polarity as thatconnected to I4. The Iarms o1 the X-ray tube actually extend ln a plane4.disposed at right angles to that of the drawing and thus are clear ofthe diffusiony pumps.

In operation of this form of migration pump abacking vpump (not shown,but connected at 2|) is iirst run and then the diffusion pumps arestarted when the pressure of the system is Ispillolently low Iforinitiation of pumping action.

2 The electrodes are then energised and power supplied to the X-raytube.

The residual gas will become ionised and will move from I3 towards I4 orI 4 according to the sign of the ionic charge. Since the electrodes areof cylindrical form the ions will on account of their kinetic energymove on into the diiiusion pumps where they may be neutralised if thepump itself comprises an electrode or may be discharged as ions into 20.If the diffusion pumps are of metal they should of course .be insulatedfrom earth potential.

In an alternative arrangement (Fig. 2) an X- ray tube 3I is mounted in asteel vessel 32 containing transformer oil 33, and iitted with a gastight lid 34. A metal extension of high vacuum connexion of a glass orporcelain migration chamber 36 extends through lid 34. Jointed toflanged ends 31, 3l' of the chamber 3B are respectively ilanged ends 38,38 of inlet conduits of diffusion pump casings 39, 39 which have outletconduits 40, 40 discharging into the gaseous space above the oilsurface. This space forms a common fore-vacuum and is maintained at therequisite low pressure by a mechanical backing pump 49 driven by anelectric motor 50 and connected to outlet 4I. Pump 49 discharges throughpipe 5I to atmosphere. External metal boilers 42, 42 are connected bymetal stand pipes 43. 43 to glass pipe sections 44, 44 terminating inmetal jet covers 45, 45 which form the electrodes of the migrationchamber and are externally connected with the high voltage supply byleads 46, 46' through vacuum-tight insulators 41, 4l.

The transformer oil in which the X-ray tube, migration chamber anddiffusion pump casings are immersed serves not only as an insulator forthe electrical leads but also to cool the condensing surfaces of thediffusion pumps and helps to seal the glass to metal joints, andprevents rise of temperature of the envelope of the X-ray tube.

In order to assist return of condensate of the diiusion pump workingfluid, which iluid is preferably an organic substance, to the boiler 42,42 the pump casings and the arms of the migration chamber may beslightly inclined as shown, whilst additionally or alternately a pip orindent 48 may be formed in the bottom Wall of the chamber to preventcollection of condensate in that part of the chamber.

The X-ray tube may if desired be exterior to the main vessel and adaptedto project rays into said vessel by way of a Window or aperture formedof any non-ray absorbing material in the vessel. To ensure that the raysare directed in the manner desired lead or lead-glass applicators may beused. In addition certain parts of the vessel may be lead lined in orderto afford protection to the operator from any rays which may otherwiseemerge from the vessel.

In other forms of construction the apparatus may include a migrationchamber of arcuate shape the ends of which discharge to a common chamberwhich may be exhausted by one diffusion pump or in some cases by othertypes of pump. Also magnetic fields may beV used additionally or inplace of the electrostatic fields for the purposes set forth.

There may be other electrodes provided in crder to give an electrostaticfocussing or accelerating effect or to improve the gas ow past diffusionpump jets or other restrictions. As an example the potential applied toan insulated jet cap may be nearer earth potential than the potential ofan adjacent electrode.

One of the migration chamber electrodes may be heated to provide anelectronic stream which may be used for initiating or augmentingionisation of residual gas. If a gas which ionises to form ions of onlyone sign of charge is to be pumped it is obvious that the migrationchamber Awill require merely one means for eduction.

The X-ray tube or insert may be formed integrally with the migrationchamber, the X-ray anode and cathode being contained in a side bulb ofsaid chamber.

The cooling of the diffusion pump may be effected by an insulated watersystem or by use of an insulating fluid such as transformer cil. Grid orother control of the X-ray tube may be effected by using a circuitresponsive to current flowing through a lead to one of the migrationchamber electrodes, whilst an indicator responsive to this current mayin some instances be used to afford a visual mea-sure of the ionicconcentration.

We claim:

1. An apparatus for producing a high vacuum, comprising means forirradiating gas to be pumped with X-rays to ionize said gas, and meansfor applying electrostatic forces to effect pumping action on theionized gas.

2. An apparatus for producing a high vacuum comprising a chamberconnected to a space to be evacuated, pumping means connected to saidchamber, means, for producing X-rays for ionising gas in said space byirradiation and means for providing an electrostatic field in saidchamber to effect migratory movement of said ionised gas towards saidpumping means.

3. An apparatus for producing a high vacuum comprising a chamber havinga high vacuum conduit adapted for connection to a space to be evacuated,two diffusion pumps disposed respectively on opposite sides of saidconduit, a forevacuum chamber into which said diffusion pumps discharge,a backing pump connected between Said forevacuurn chamber andatmosphere, means for producing X-rays for ionising gas in said space byirradiation and means for providing an electrostatic field in saidchamber to effect migratory movement of said ionised gas towards saiddiffusion pumps.

fi. An apparatus for producing a high vacuum comprising a chamber havinga high vacuum conduit adapted for connection to a space to be evacuated,two diffusion pumps disposed respectively on opposite sides of saidconduit, a forevacuum chamber into which said diffusion pumps discharge,a backing pump connected between said forevacuum chamber and atmosphere,means for producing X-rays for ionising gas in said space by irradiationand electrodes of cylindrical form disposed in said chamber andmaintained at different electrostatic potentials as to provide anelectrostatic eld in said chamber to effect migratory movement of saidionised gas towards said diffusion pumps.

5. An apparatus for producing a high vacuum comprising a chamber havinga high Vacuum conduit adapted for connection to a space to be evacuated,two diffusion pumps disposed respectively on opposite sides of saidconduit, a forevacuum chamber into which said diffusion pumps discharge,a backing pump connected between said forevacuum chamber and atmosphere,an X-ray generator disposed in said chamber for ionising gas in saidspace by irradiation, and electrodes of cylindrical form disposed insaid chamber and maintained at different electrostatic potentials so asto provide an electrostatic field in said chamber to effect migratorymovement of said ionised gas towards said diffusion pumps.

6. An apparatus for producing a high vacuum, comprising a chamber havinga high vacuum conduit adapted for connection to a space to be evacuated,two diffusion pumps having nlets connected to said chamber respectivelyon opposite sides of said conduit, a forevacuum enclosure into whichSaid diffusion pumps discharge, a backing pump connected between saidforevacuum enclosure and atmosphere, means for irradiating gas in saidspace with X-rays to ionise said gas, and means for providing anelectrostatic field in said chamber to effect migratory movement of saidionised gas towards said diffusion pumps.

'7. An apparatus for producing a high vacuum, comprising a, chamberhaving a highvacuum conduit adapted for connection to a space to beevacuated, two diffusion pumps having inlets connected to said chamberrespectively on opposite sides of said conduit, 'a forevacuum enclosureinto which said diffusion pumps discharge, a backing pump connectedbetween said forevacuum enclosure and atmosphere, means for irradiatinggas in said space with X-rays to ionise said gas, and electrodes ofcylindrical form disposed in said chamber and maintained at differentelectrostatic potentials for providing an electrostatic field in saidchamber to effect migratory movement of said ionised gas towards saiddiffusion pumps.

S. An apparatus for producing a high vacuum, comprising a chamber havinga high vacuum conduit adapted for connection to a space to be evacuated,two diffusion pumps having inlets connected to said chamber respectivelyon opposite sides of said conduit, a forevacuum enclosure into whichsaid diffusion pumps dis'- charge, a backing pump connected between saidforevacuum enclosure and atmosphere, an X-ray generator for ionising gasin said space by irradiation, and electrodes of cylindrical formdisposed in said chamber and maintained at different electrostaticpotentials for providing ari-electrostatic field in said chamber toeffect migratory movement of said ionsied gas towards said diffusionpumps.

9. An apparatus for producing a high vacuum, comprising a chamber havinga high vacuum conduit adapted for connection to a space to be evacuated,two diffusion pumps having 1nletsconnected to said chamber respectively0n opposite sides of said conduit and Jet assemblies projecting throughsaid inlets into said chamber, an enclosed vessel containing saidchamber and a part of each of said diffusion pumps together with aninsulating uid such as transformer oil surrounding said parts of thediffusion pumps for cooling the same, the gaseous space above the fluidin said vessel constituting a forevacuum enclosure into which saiddiffusion pumps discharge, a backing pump connected between saidforevacuum enclosure and atmosphere, an X-ray generator disposed in saidchamber for ionising gas in said space by irradiation, and electrodesconstituted by part of each jet assembly in said chamber and maintainedat different electrostatic potentials so as to provide an electrostaticfield in said chamber to effect migratory movement of said ionised gastowards said diffusion pumps.

10. An apparatus according tc claim 9 in which there is provided anupwardly extending indent in the bottom wall of the chamber to preventcollection of working fluid condensate in the chamber.

11. An apparatus for the production of high vacua comprising an enclosedvessel, an insulating liquid such as transformer oil partly lling saidvessel, a generally cylindrical chamber disposed in said liquid andhaving end portions emerging through the walls of said vessel, a bttomwall sloping downwardly towards said end portions, diffusion pumpsformed integral with said chamber one near each end portion thereof andadapted to discharge gas into said vessel above the liquid leveltherein, a backing pump connected to the vessel to exhaust gascollecting above said liquid level, a conduit of diameter 6substantially equal to that of said chamber ex'-l tending from thecentre of said chamber and emerging outside said vessel and adapted tobe connected to a space to be evacuated, electrodes on opposite sides ofsaid conduit in said chamber adapted to be charged to differentelectrostatic potentials, and an X-ray generator arranged below theliquid level in the vessel to irradiate gas in said chamber, conduit andspace to be evacuated.

l2. An apparatus for the production of high vacua, comprising anenclosed vessel, an insulating liquid such as transformer oil partlylling said vessel, a generally cylindrical chamber disposed in saidliquid and having end portions emerging through the walls of saidvessel, a bottom wall sloping downwardly towards said end portions,diffusion pumps formed integral with said chamber one near each endportion thereof and adapted to discharge gas into said vessel above theliquid level therein, an umbrella jet deflector of metal forming part ofeach diffusion pump, a backing pump connected to the vessel to exhaustgas collecting above said liquid level, a conduit extending from thecentre of said chamber and emerging outside said vessel and adapted tobe connected to a space to be evacuated, electrodes constituted by saiddeflectors on opposite sides of said conduit in said chamber adapted tobe charged to different electrostatic potentials, and an X-ray generatorarranged below the liquid level in the vessel to irradiate gas in saidchamber, conduit and space to be evacuated.

JOHN WM. TILLS.

JOHN B. LOVATT F. C. POTTS.

